A variable vane arrangement for a turbomachine, as disclosed in our UK patent application GB2339244A, comprises a plurality of circumferentially arranged vanes, a plurality of operating levers and a control ring. Each vane comprises an upstream portion secured to a casing and a movable downstream portion pivotally mounted to the casing of the turbomachine. Each operating lever is pivotally mounted at a first end to the control ring and each operating lever is mounted at second end to a spindle of the movable downstream portion of a respective one of the vanes. Rotation of the control ring causes the levers to adjust the angular position of the movable downstream portions of the vanes.
In this variable vane arrangement the movable downstream portions of the vanes are pivotally mounted about an axis adjacent the upstream ends of the movable downstream portions and downstream of the downstream ends of the fixed upstream portions of the vanes.
Also in this variable vane arrangement the radially outer ends of the downstream ends of the upstream portions of the vanes are shaped to allow the radially outer ends of the upstream ends of the movable downstream portions of the vanes to be inserted into apertures in the casing.
A problem with this variable vane arrangement is that when each vane is fully assembled, there is an undesirable gap between the shaped radially outer end of the downstream end of the fixed upstream portion of the vane and the radially outer end of the upstream end of the movable downstream portion of the vane. In operation these gaps allow a leakage flow from the concave pressure surfaces to the convex suction surfaces of the vanes which may be a source of aerodynamic forcing, or aeromechanical excitation, on the stage of rotor blades downstream of the vanes. The aerodynamic forcing may cause the rotor blade to vibrate and reduce the working life of the rotor blade.